Anomalous elasticity: from phase transitions to flexible electronics

• Applicant: Professor Dr. Jörg Schmalian
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429701487

The primary goal of the project is to study theoretically anomalous elastic, electronic, and magnetic properties of free-standing membranes of two-dimensional (2D) materials. Owing to their dynamic (flexural phonons) and static (ripples, wrinkles) out-of-plane deformations, 2D membranes exhibit peculiar properties such as nonlinear Hooke’s law, negative thermal expansion coefficient which remains constant down to ultralow temperatures, negative Poisson ratio (auxeticity), and anomalous softening of the bulk and shear moduli. Development of possible applications of 2D materials, e.g., in the emerging field of flexible nano-electronics, requires a deeper understanding of the interplay between the anomalous elasticity and electronic structure, including the feedback of electronic correlations on the nano-mechanics of membranes. The mutual influence of elastic and electronic properties of 2D materials is the focus of the project. The key research objectives are (i) to develop a theoretical description of realistic membranes hosting correlated electrons, with the emphasis on possible interaction-induced phase transitions as well as anomalous stress-dependence of membrane resistivity; (ii) to investigate the interplay of mechanical, electronic, and magnetic properties of membranes, going beyond the perturbation theory and accounting for pseudogap formation and polaronic effects; and (iii) to study the feedback of elastic properties on electronic degrees of freedom in correlated Moiré superlattices, such as twisted bilayer graphene. The envisioned outcome of the project is a new knowledge base, quantifying the anomalous elastic and transport properties of 2D materials that could be used in electronics, plasmonics, and photonics. Potential applications include superconduciting devices based on twisted graphene, resistive and thermal switches based on controlling the amplitude of flexural phonons via external strain, broadband infrared radiation detectors based on mutual coupling between conduction electrons and out-of-plane dynamical elastic modes (flexural phonons) and static corrugations (ripples), and new types of nanoelectromechanical devices. The consortium consists of theoretical groups in Russia and Germany that all possess significant expertise and international visibility in the field. The Russian and German groups have established cooperation in the fields of graphene, disordered and strongly-correlated systems, and critical phenomena. Joint development of this novel research trend forms a basis for lasting collaboration. The expertise of the German group in the study of strongly correlated phenomena and superconductivity will be complemented by the expertise of the Russian team in the field of anomalous elastic properties of crystalline membranes, providing additional guarantee for the successful implementation of the project.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Professor Dr. Valentin Kachorovskii, until 3/2022